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MEMOIR 

OF 

JOHN MICHELL 



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MEMOIR 

OF 

JOHN MICHELL 

M.A., B.D., F.R.S. 

Fellow of Queens' College, Cambridge, 1749 

Wood war Jian Professor of Geology 

in the University 1762 

BY 

SIR ARCHIBALD gEIKIE 

O.M, K.C.B, D.CJ.., D.Sc^ F.R.S. 



CAMBRIDGE 
AT THE UNIVERSITY PRESS 



JOHN MICHELL 

AMONG the men of science in England 
during the latter half of the eighteenth 
century there was one specially remark- 
able for the wide range of his genius and 
the originality of his methods of research. 
As Rector of a quiet country parish in 
Yorkshire, he lived remote from the centre 
of the intellectual life of his day, but in 
that retreat he had time and opportunity 
for reflection and experiment. Moreover, 
as he was able to visit London each year, 
he could keep in touch, not only by cor- 
respondence but by personal contact, with 
the leaders of enquiry. Though much 
esteemed and respected by his contem- 
poraries, he has perhaps hardly received 
from subsequent generations the recog- 
nition lo which the merit of his work 
justly entitles him. It is true that some 

G. I 



historians who have recorded the progress 
of the sciences to which he devoted his 
attention have alluded more or less fully 
to his published papers. But it is not 
until a review is made of his contributions 
to each of the sciences of geology, physics 
and astronomy that an adequate concep- 
tion can be formed of the place that is due 
to him in the history of English science. 
Recent researches among the archives 
of the Royal Society and of its dining 
Club brought the name of this modest 
investigator so frequently before me as to 
rouse my interest in his career. I was 
induced to search for any personal details 
regarding him that might still be recover- 
able, and to peruse such of his writings as 
I had not previously read. As the result 
of this enquiry I have thought it to be 
my duty to bring his life and his solid 
achievements in science more promi- 
nently to notice. Hence the origin of 
the present Memoir. 



JOHN MICHELL, the friend of Henry 
Cavendish and Joseph Priestley, has left 
no record of his life beyond his published 
writings. A few of his letters have sur- 
vived. Several of them addressed to Sir 
William Herschel have been found among 
that philosopher's manuscripts, and are 
quoted in the collected edition of his 
Papers. A long and hitherto unpublished 
letter from Michell to Cavendish has 
been preserved among the papers of that 
great man, and is inserted in the present 
Memoir 1 . 

It is not quite certain where and when 
Michell was born. Probably his native 
place was Nottingham, and the year of 
his birth 1 724. Of his parentage nothing 
appears to be known. The earliest 
accounts of him which have been re- 
covered are preserved in the registers of 

Queens' College, Cambridge, where a full 



1 This letter was known to Dr George Wilson, 
Cavendish's biographer, and is referred to by him 
in the Life (portea^ p. 47). 

3 



record has been kept of his College life, 
from the time of his admission as Pen- 
sioner on 1 7th June 1742, until, after 
taking his degrees and filling many offices 
during a residence of twenty-one years, 
he quitted Cambridge for a rectory in the 
country 1 . He is entered in these records 
as from Nottingham. 

The year after his reception into 
Queens' he was elected Bible-Clerk and 
held this office for two years. Again for 
three years, from 1 747 to 1 749 he filled the 
same post 2 . Heclid not take his Bachelor's 
degree until 1748. His name appears as 
fourth wrangler in the list for 1748-9, 
which was the second competition after 
the institution of the wranglership. On 
3Oth March 1749 he was chosen Fellow 

1 The present President of Queens' College, 
the Rev. T. C. Fitzpatrick, has been so good as to 
collect for me all the details of College life that are 
here given. 

2 The duty of this officer appears to have been 
to read the Bible in hall, for which a remuneration 
of one shilling a week was allowed, afterwards slightly 
increased. 



of his College. Thereafter for some 
fifteen years he continued to fill various 
lectureships and other offices at Queens'. 
He was Tutor of the College from 
1751 to 1 763 ; Praelector in Arithmetic in 
1751 ; Censor in Theology in 17524; 
Praelector in Geometry in 1753 ; Prae- 
lector in Greek in 1755 and 1759; Senior 
Bursar in 1 7568 ; Praelector in Hebrew 
in 1759 and 1762 ; Censor in Philosophy 
and Examiner in 1760. He took his 
degree of Master of Arts in 1752 and 
Bachelor of Divinity in 1761. He was 
nominated Rector of St Botolph's, Cam- 
bridge, on 28th March 1760, and held 
this living until June 1763, when he left 
Cambridge on being collated to a rectory 
in the country. 

The registers of Queens' College furnish 
information as to the modest payments 
made in the eighteenth century to the 
officials by whom the work of the College 
was performed. In Michell's case we 
learn that the largest sum paid to him as 

5 



Bible-Clerk was 5. 3-r. lod. for the year 
1748. Again in 1753 his stipend as Fellow 
amounted to 9, that of his theological 
Censorship to 8, and that of his ex- 
aminership to 2. 

Besides these College duties he held 
from time to time some University 
appointments. In July 1754 he was 
elected to the office of Moderator for the 
following year. In 1 75 5 he was appointed 
Taxator 1 and on 24th June 1762 Scrutator 
for the following year. But the most im- 
portant office conferred upon him was the 
Woodwardian Professorship of Geology, 
to which, near the end of the year 1762, 
he was appointed by Colonel King, the 
last surviving executor of John Woodward 

1 The Master of St John's informs me that "the 
Taxators were appointed by the Colleges according 
to the cycle for Proctors. They regulated the markets, 
examined the assize of bread, the lawfulness of 
weights and measures, and called all abuses and 
defects into the court of the Commissary. The 
Scrutators seem to have been assistants to the Proctors. 
The Proctors read the Graces and took the votes in 
the Regent House ; the Scrutators did the like in 
the Non-Regent House." 

6 



who by his will dated in 1727 founded 
the Chair. Michell did not hold the office 
for quite two years, having to vacate it 
on his marriage in 1 764. There appears 
to be no evidence that during his short 
. tenure of the office he ever gave geological 
lectures 1 . But the intimate acquaintance 
with geological phenomena shown in his 
essay on Earthquakes, communicated to 
the Royal Society in the spring of 1760, 
proves that he was well qualified to lecture 
on a subject which he had pursued with 
zeal in the field. It is difficult to believe 
that he did not Impart to his under- 
graduate friends some of the knowledge 
which he had gained in many traverses 
across the southern counties, if indeed he 
did not take them with him in some of 
his rambles. 

A brief description of MichelFs per- 
sonal appearance in his College days, 
penned by a contemporary diarist and 
preserved among the manuscripts of the 

1 Life of Adam Stdgwick^ vol. I, p. 192. 

7 



British Museum, may be quoted here. 
"John Michell, BD is a little short Man, 
of a black Complexion, and fat ; but 
having no Acquaintance with him, can 
say little of him. I think he had the Care 
of St Botolph's Church, while he con- 
tinued Fellow of Queens' College, where 
he was esteemed a very ingenious Man, 
and an excellent Philosopher. He has 
published some Things in that way, on 
the Magnet and Electricity V 

Although his time was evidently much 
engaged in the various official duties that 
devolved upon him in Cambridge, there is 
proof that he had already launched upon 
his career of physical research and experi- 
mentation within the walls of his College. 
In 1750, the year after he obtained his 
Fellowship and when he was some six- 
and-twenty years of age, he published at 
Cambridge a little volume on Artificial 
Magnets to which further reference will 

1 Cole MSS. XXXIH, 156 (Add. MSS. Mus. 
Brit., 5834). 

8 



be made on a later page. As he was fond 
of constructing his own apparatus, his 
rooms at Queens' with all his implements 
and machinery would sometimes wear the 
look of a workshop, and were no doubt 
the theme of much amused wonderment 
among both Fellows and undergraduates. 
But these mechanical operations and 
experiments indoors were only a part of 
the scientific occupations with which he 
employed his leisure. As above stated, 
there can be no doubt that he was in the 
habit of making what would now be 
called geological excursions, in which he 
interested himself in noting the distri- 
bution and sequence of the rock-forma- 
tions in the southern counties of England. 
It was only by such practical field-work 
that he could gain the remarkably accu- 
rate conception of the structure of the 
stratified portion of the earth's crust em- 
bodied in his Earthquake paper of 1760. 
This epoch-making essay was read to the 
Royal Society in sections at five successive 

9 



evening meetings. The active College 
Preceptor and Bursar was now introduced 
into the centre of the scientific life of 
the time, where he was warmly wel- 
comed. Immediately after the reading 
of the first portion of his paper some of 
the Fellows of the Society drew up and 
signed a certificate in favour of his elec- 
tion into the Society. Within a fort- 
night, and before the reading of his paper 
was ended, the certificate was in the 
hands of the Council. It ran as follows : 

The Rev. Mr John Michell M.A. Fellow 
of Queens' College, Cambridge, who has re- 
commended himself to the Publick by his 
Experiments in Magnetism, and has lately 
communicated to this Society a Dissertation 
upon Earthquakes, being very desirous of the 
honour of becoming a member of the Royal 
Society, We, whose names are underwritten, 
recommend him as a gentleman extremely 
well qualify 'd for that honour. 

LONDON, March 6, 1760 

The first names on the list of signa- 
tures are those of the Secretary of the 
10 



Society, Dr Thomas Birch, and of Mi- 
chell's contemporary at Queens' College, 
the active and broad-minded Sir George 
Savile, Bart., who, after serving in his 
youth against the Jacobite rebels in 1745, 
spent a busy and useful life in Parliament 
as member for Yorkshire. Next comes 
the name of Dr Gowin Knight, Copley 
Medallist, and first Principal Librarian 
of the British Museum, whose researches 
in magnetism would especially draw him 
towards Michell. The other signatures 
include those of Dr Matthew Maty, 
afterwards Secretary of the Royal Society 
and Principal Librarian of the British 
Museum ; Daniel Wray, the antiquary ; 
and John Hadley, another of the Fellows 
of Queens' College, who a few years 
before had been appointed Professor of 
Chemistry at Cambridge, and with whom 
Michell would doubtless have much dis- 
cussion of scientific matters. Michell 
was duly elected a Fellow of the Royal 
Society on 1 2th June 1 760. It is worthy 

ii 



of notice that the immediately preceding 
election was that of Henry Cavendish, 
and that the two names stand together 
in chronological sequence in the Record 
of the Society. 

In the spring of the year 1763 Michell 
gave up his residence at Cambridge and 
became Rector of Compton in the valley 
of the Itchin, which winds from Win- 
chester to the sea. It was not improbably 
with a view to his marriage that this 
change of abode was made. The follow- 
ing announcement appeared in the Cam- 
bridge Chronicle of 8th September 1764. 
" A few days ago the Rev. Mr Michell, 
Rector of Compton, near Winchester, 
late Fellow of Queens' College, Cam- 
bridge, and Woodwardian Professor of 
Fossils in this University, was married 
to Miss Williamson, a young lady of 
considerable fortune, near Newark in 
Nottinghamshire." He did not long 
retain his living at Compton, for on 
23rd January 1765, he was collated 
12 



Rector of Havant, Hants. The prospect 
of a happy married life at this home was 
rudely dissipated in the autumn of that 
same year, when his young wife died at 
Newark 1 . Two years later, on 3rd Oc- 
tober 1 767, he was instituted Rector of 
Thornhill, near Dewsbury in Yorkshire, 
and remained in this office as long as he 
lived. He subsequently married again 2 . 
He appears to have had only one child, 
a daughter, probably by his first wife. 
This daughter married and is said to have 
died at an advanced age somewhere about 
the year 1840. 

In the summer of 1871 there appeared 
in the journal called the English Mechanic* 
a communication which gave some pre- 
viously unpublished information about 
John MichelL As the writer of the letter 
stated that he was the great-grandson of 

1 Cambridge Chronicle, 1 2th October 1765. 

* In the church at Thornhill, the burial register 
records that Ann Michell, relict of the late Rev. 
J. Michell, Rector, died 6th November 1818. 

1 Vol. xiu, p. 310 (i6th June 1871). 

'3 



the philosopher, and that he derived 
his information from his grandmother, 
Michell's daughter, considerable import- 
ance has naturally been attached to his 
contribution, and its statements have been 
quoted, though sometimes with hesita- 
tion, in various biographical notices of 
his eminent ancestor. It ran as follows : 

After William Herschel's appointment as 
organist of Halifax, he became acquainted 
with the Rector of Thornhill, (a village about 
nine miles from Halifax and six from Wake- 
field) whose name was John Michell a man 
of fortune, whose whole life was devoted to 
science, and whose writings are to be found 
in considerable numbers in the journals of the 
Royal Society, during the latter half of the 
last century, one of the most prominent papers 
being that on the great Lisbon Earthquake 
of 1 755. John Michell may perhaps be better 
known rs the builder of the mathematical 
bridge across the Cam at Queens' College, 
Cambridge 1 . He was no mean violinist in 

1 This family tradition is probably an exaggera- 
tion of any connection which Michell may have 
had with, the bridge. He obtained his Fellowship 
at Queens' on 3Oth March 1749. In October of 
that year it is recorded in the Magnum Journale of 



his day, and his soirees where not only the 
first musical talent, but also the first scientific 
men of the day, such as Cavendish, Black 
and Priestley used to meet occasionally were 
well known in the West Riding of Yorkshire, 
and to which Wm Herschel used to come to 
perform on the violin. At the period of 
these visits Michell was and had long been 
engaged in making what was at that time a 
large telescope a ten-foot reflector. The 
perfect combination for a perfect reflector, 
and the grinding the same, had long occupied 
MichelFs attention, in which he at last suc- 
ceeded, and I believe I am correct in saying 
that Herschel there became a willing and able 
pupil, and obtained the germs of his great 
astronomical renown. At the death of John 
Michell, all his scientific apparatus were sent 
to Queens' College, Cambridge, save and ex- 
cept his large reflecting telescope, which by 
purchase or gift came into the possession of 
Wm Herschel. I have been told by the only 

the College that Mr Etheridge was paid 21 for 
the design and model of the bridge. The construc- 
tion was not completed until September of the fol- 
lowing year when the cook was paid 175. <)d. for a 
supper to the workmen on finishing their work. 
Michell could not fail to be interested in the opera- 
tions, and may quite possibly have been able to give 
useful help to the designer, as well as to James Essex, 
the builder of the bridge. 

15 



child of Michell, who died about thirty-five 
years ago, at the age of upwards of eighty, 
and was intimate with Herschel, that he told 
her that the principal part of his observations 
had been made with her father's telescope, 
which he found more convenient than his 
own larger one. The Rev. John Michell, I 
have also been informed, was the inventor of 
an apparatus for ascertaining the weight of the 
world, which is known as that of Cavendish 
I am the grandson of Michell's only daughter, 
from whom I heard much, and I was also a 
pupil, more than fifty years ago, of an old 
clergyman, who had in early life been for 
several years the curate of Thornhill under 
Michell. [Signed] Khoda Bux. 

That the memory of the daughter or 
that of the great-grandson, or of both 
together, had failed can easily be proved. 
Some of the statements in the communi- 
cation are curiously inaccurate. William 
Herschel undoubtedly passed some of his 
early years in Yorkshire where he played 
the hautboy in the band of the Durham 
militia and performed on the violin at 
public concerts in Wakefield and Halifax. 
The family tradition that Michell was 
16 



<c 



no mean violinist' 2 and that he gave 
musical parties is not improbably true. 
But it appears to be quite certain that he 
and Herschel did not make acquaintance 
with each other in Yorkshire, and that 
the Rector of Thornhill did not instruct 
the future illustrious astronomer in the 
art of grinding specula. Herschel was 
appointed organist at Bath in the autumn 
of 1766 and removed to that city at the 
beginning of the following year, before 
Michell succeeded to the living at Thorn- 
hill. There was thus no opportunity for 
their meeting in Yorkshire. Herschel at 
Bath was absorbed in his duties as a pro- 
fessional musician and did not enter upon 
the study of astronomy till 1773, and next 
year began to grind specula. The two 
men had never met nor exchanged letters 
up to the spring of the year I78I 1 . 

The legend that the discoverer of the 
planet Uranus received his first lessons in 

1 Scientific Papers of Sir William Herschel (1912), 
vol. i, p. xxxii. 

C. I 7 



telescope construction from the learned 
Rector of Thornhill must thus be dis- 
missed as unfounded. Each of these two 
men of science worked independently 
and ground his own mirrors. They 
were first brought into correspondence 
with each other through the medium of 
Dr Wm Watson, F.R.S., who, being at 
Bath and knowing Herschel there, sent 
to Michell an account of what the astro- 
nomer had been doing. On 2 1 st January 
1781, Michell replied: "I look upon 
myself as very much obliged to you for 
your favour from Bath, and particularly 
for the very interesting account, both of 
what Mr Herschel has done and what 
he has seen, both of which seem to be 
very important. I shall be very happy if 
I should be able to succeed as well, or 
near as well, as from your account he 
seems to have done, and I should be very 
glad of the favour of his correspond- 
ence : at the same time I think it very 
probable that I may be more likely to 
18 



learn from him what may be useful to 
myself, than he to learn anything from 
me 1 ." A brief correspondence followed 
between the two astronomers, but they 
probably met occasionally at the Royal 
Society's rooms, the table of the Royal 
Society Club, or other meeting places in 
London. 

The search for further personal records 
of the Rector of Thornhill has not been 
successful. His life in the Yorkshire 
parish was doubtless quiet and uneventful, 
full of pastoral duty, well discharged, but 
with leisure for the prosecution of scien- 
tific work. This work was undertaken 
for its own sake, and much of it was pro- 
bably never published, though it was 

1 Scientific Papers of Sir IVilliam Herschel, vol. I, 
pp. xxxi, xxxii. The two astronomers never met 
nor exchanged letters before I2th April 1781, on 
which date Michell addressed a letter to Herschel 
dealing with mirrors, and the relative merits of dif- 
ferent types for large and small apertures. Op. clt. 
p. xxxii. It is interesting to know, from the testi- 
mony of Herschel himself, that after Michell's death, 
he purchased his large telescope. See postca y p. 96. 

'9 



always at the service of any fellow-worker 
interested in the same subjects. Though 
living so far from London, Michell was 
nevertheless able to maintain intimate 
relationship with some of the most emi- 
nent men of science of his time. He 
appears to have had some appointment 
or duty which for a number of years 
took him annually to London, and gave 
him the opportunity of attending the 
meetings of the Royal Society and culti- 
vating the companionship of his scientific 
friends. From the year 1758 onwards 
till towards the close of his life he con- 
tinued to be a frequent guest at the 
weekly dinners of the Royal Society Club. 
There would seem, indeed, to have been 
a kind of friendly rivalry among the 
members of the Club in securing him as 
a guest at these dinners, and in this social 
competition his friend Henry Cavendish 
took part. Thus during the summer of 
1784 he dined seven times with the Club. 
Two years later, when he spent the 
20 



months of May and June in the Capital, 
he was a guest every week during his 
stay, and similar hospitality awaited him 
at the " Crown and Anchor " tavern as 
long as he lived 1 . 

During his journeys from and to his 
Yorkshire home, now by one route, now 
by another, on horseback or by carriage, 
or in such public coaches as then plied 
on the roads between London and the 
Midlands, Michell appears to have paid 
close attention to the outcrops and suc- 
cession of the rock-formations across 
which he travelled. There was probably 
no one else so familiar as he with the 
various quarries, pits and other exposures 
of these rocks to be seen from the high 
roads. In the leisurely fashion of those 
days he would sometimes halt for a night 
or two on the way, and on these occasions 
would take advantage of the opportunity 
of obtaining the evidence to be found in 

1 Annah ef tti Royal Society Club^ pp. 74, 77, 
165. 

21 



any fresh opening of the ground. By 
these means and by special excursions for 
the purpose of geological investigation 
which as we have seen he began to make 
in his College days, he acquired a broader 
and more accurate conception of the 
geological structure of the southern half 
of England than any of his predecessors. 
Moreover, his rectory lay in the heart of 
the great Yorkshire coal-field where the 
progress of the mining industry continu- 
ally brought geological questions to his 
notice. 

It was at Thornhill, during the leisure 
which his clerical duties permitted, that 
he was able to carry on those important 
investigations in physics and astronomy 
with which his name will always be 
associated. In the same quiet retirement 
he devised and constructed the various 
forms of original and ingenious apparatus, 
with which he solved or illustrated the 
problems that presented themselves to his 
ever active intellect. He continued to 

22 



reside at Thornhill till his death on 
2ist April 1793 in the sixty-ninth year 
of his age 1 . 

In reviewing the scientific work ac- 
complished by John Michell it will be 
convenient to consider it in three sec- 
tions : first, his contributions to Geology ; 
second, his contributions to Physics ; and 
third, his contributions to Astronomy. 

1 MichelFs tombstone at Thornhill records in 
characteristic eighteenth century language his life, 
work and character : "In the Chancel of this Church 
are deposited the Remains of the Rev d . J n . Michell, 
B.D., F.R.S., and 26 years Rector of this Parish. 
Eminently distinguished as the Philosopher and the 
Scholar, he had a just claim to the character of the real 
Christian, in the relative and social duties of life. 
The tender Husband, the indulgent Father, the affec- 
tionate Brother and the sincere Friend were promi- 
nent features in a character uniformly amiable. His 
Charities we re not those of Ostentation, but of feeling; 
His strict discharge of his Professional duties, that 
of principle, not form. As he lived in possession of 
the esteem of his Parishioners, so he has carried 
with him to the grave their regret. He died the 
21 st April 1793, in the 69* year of his age.*' 



I 

CONTRIBUTIONS TO GEOLOGY 

THE subject of the structure of the earth's 
crust appears to have engaged Michell's 
attention long before he left Cambridge, 
though in this as in other investigations, 
he was in no hurry to publish his obser- 
vations. He was ultimately led to embody 
the results of his studies in this subject 
in the paper on Earthquakes which he 
communicated to the Royal Society in 
the spring of the year I76O 1 . This re- 
markable Essay is not only a dissertation on 
earthquakes, but contains an exposition 
of the structure of the terrestrial crust 

1 The full title of this paper was as follows : 
"Conjectures concerning the Cause, and Observa- 
tions upon the Phaenomena of Earthquakes ; particu- 
larly of that great Earthquake of the first of November 
1755 which proved so fatal to the City of Lisbon, 
and whose Effects were felt as far as Africa, and more 
or less throughout almost all Europe ; By the 
Reverend John Michell M.A. Fellow of Queens' 
College, Cambridge." It appeared in vol. 51 (1760) 
of the Philosophical Transactions^ pp. 566-634. 

24 



which he had worked out in the course 
of his journeys and excursions from Cam- 
bridge over the southern counties of 
England. As this stratigraphical work 
was continued through the rest of his life 
I shall consider it in detail after first 
dealing with the portion of the paper 
more immediately concerned with the 
cause and phenomena of earthquakes. 

i. The Cause and Phenomena of 
Earthquakes 

The attention of the civilised world 
was strongly drawn to the long series of 
earthquakes which culminated in the 
appalling catastrophe that overwhelmed 
Lisbon and shook the greater part of 
Europe on ist November 1755. Many 
accounts of the facts as well as attempted 
explanations of them were printed in the 
current literature of the time. In par- 
ticular, the Royal Society devoted the 
forty-ninth volume of the Philosophical 
Transactions to a large collection of 



reports on the subject. By far the most 
important contribution to the scientific 
discussion of the nature and cause of 
these earth-tremors was this paper by 
Michell. It contained the first attempt 
to suggest a natural cause of earthquakes, 
and to explain the nature of seismic 
movements. 

In attacking the problem Michell 
started with the fundamental postulate 
of the existence of " subterranean fires." 
It was the general belief of the day, which 
he shared, that these "fires* 3 resulted 
from the spontaneous ignition of pyritous 
inflammable strata, such as coals and car- 
bonaceous shales lying at variable dis- 
tances beneath the surface of the earth. 
Werner and his followers were so con- 

. 

vinced that such was the origin of these 
"fires," to which they attributed the 
existence of volcanoes, that they believed 
volcanic action to be of comparatively 
late date in the history of the globe, seeing 
that it could not arise till vegetable 
26 



growths had long flourished on the earth 
and been buried under sediments to be- 
come beds of coal. Michell argued that 
if a large body of water should be let 
down suddenly upon one of these fires 
a vapour would be produced, the quantity 
and elastic force of which might be fully 
sufficient to account for the origin of 
earthquakes. He pointed out the fre- 
quency of these concussions in volcanic 
districts and, like the Wernerian geo- 
gnosts, he connected the phenomena of 
volcanoes with the same subterranean 
fires, the vents and craters marking the 
position of weaker portions of the outer 
shell of the earth across which the vapour 
generated below could force its way to 
the surface, often carrying with it an out- 
pouring of molten material. The energy 
with which this escape was effected 
appeared to him to be evident from the 
vast size of the blocks of rock projected 
during volcanic eruptions and the great 
distances to which such masses of stone 

27 



were often thrown. "If," he asked, 
"when the vapours find a vent, they are 
capable of shaking the country to the 
distance of ten or twenty miles round, 
what may we not expect from them when 
they are confined? ' 

He stated that " the motion of the 
earth in earthquakes is partly tremulous, 
and partly propagated by waves which 
succeed one another, sometimes at larger, 
sometimes at smaller distances, and this 
latter motion is generally propagated 
much further than the former 1 ." He 
believed that both of these motions could 
be accounted for by the steam generated 
as assumed. " Let us suppose," he re- 
marked, " the roof over some subter- 
raneous fire to fall in. The earth, 
stones, etc., of which it was composed 
would immediately sink in the melted 
matter of the fire below : hence all the 



1 Art. 1 1 of the paper. Michell appears to have 
been the first to point out that the earthquake travels 
in successive waves through the earth. 

28 



water contained in the fissures and 
cavities of the part falling in would come 
in contact with the fire and be almost 
instantly raised into vapour. From the 
first effort of this vapour, a cavity would 
be formed (between the melted matter 
and superincumbent earth) filled with 
vapour only, before any motion would 
be perceived at the surface of the earth : 
this must necessarily happen, on account 
of the compressibility of all kinds of earth 
and stones, etc.; but as the compression 
of the materials immediately over the 
cavity would be more than sufficient to 
make them bear the weight of the super- 
incumbent matter, this compression must 
be propagated on account of the elasticity 
of the earth in the same manner as a pulse 
is propagated through the air. And 
again, the materials immediately over 
the cavity, restoring themselves beyond 
their natural bounds, a dilatation will 
succeed to the compression; and these 
two following each other alternately, for 

29 



some time, a vibratory motion will be 
produced at the surface of the earth. If 
these alternate dilatations and compres- 
sions should succeed one another at very 
small intervals, they would excite a like 
motion in the air and thereby occasion 
a considerable noise. The noise that is 
usually observed to precede or accompany 
earthquakes, is probably owing partly to 
this cause, and partly to the grating of 
the parts of the earth together, occasioned 
by that wave-like motion before men- 
tioned " (Art. 6)\ 

" As a small quantity of vapour almost 
instantly generated at some considerable 
depth below the surface will produce a 
vibratory motion, so a very large quantity 
(whether it be generated almost instantly, 
or in any small portion of time) will pro- 
duce a wave-like motion. The manner 
in which this wave-like motion will be 
propagated may, in some measure, be 
represented by the following experiment. 
Suppose a large cloth or carpet (spread 
30 



upon a floor) to be raised at one edge, 
and then suddenly brought down again 
to the floor ; the air under it, being by 
this means propelled, will pass along, till 
it escapes at the opposite side, raising the 
cloth in a wave all the way as it goes. 
In like manner, a large quantity of vapour 
may be conceived to raise the earth in 
a wave, as it passes along between the 
strata, which it may easily separate in 
an horizontal direction, there being, as 
I have said before, little or no cohesion 
between one stratum and another. The 
part of the earth that is first raised, being 
bent from its natural form, will en- 
deavour to restore itself by its elasticity, 
and the parts next to it, beginning to 
have their weight supported by the 
vapour, which will insinuate itself under 
them, will be raised in their turn, till it 
either finds some vent, or is again con- 
densed by the cold into water, and by 
that means prevented from going any 
further" (Art. 58). 

3' 



It is thus evident that Michell con- 
ceived the vapour to continue to force 
its way onward between the strata as far, 
at least, as the earthquake continued to 
be felt at the surface. His familiarity 
with the regular and gently inclined 
stratification of the rocks in the southern 
part of England, and his experience that 
at the surface of the ground they may 
for the most part be easily split open 
along their bedding-planes led him to 
this belief. He imagined that the vapour 
might be propelled even to the extreme 
limits of the area affected by an earth- 
quake, for he remarks in one place that 
" the shortest way that the vapour could 
pass from Lisbon to Loch Ness was under 
the Ocean" (Art. 98 note). 

The same ingenious paper showed how 
the centre or focus from which an earth- 
quake is propagated may be ascertained 
first, from observation of the different 
directions from which the shock arrives 
at several distant places : " if lines be 
32 



drawn in these directions the place of 
their common intersection must be nearly 
the place sought"; secondly, from the 
time of arrival of the earthquake at 
different places; and thirdly, from the 
successive arrivals of the great sea-wave. 
The greatest degree of exactness is ob- 
tainable " in those cases where earth- 
quakes have their source from under the 
ocean, for the proportional distance of 
different places from that source may be 
very nearly ascertained by the interval 
between the earthquake and the succeed- 
ing wave : and this is the more to be 
depended on, as people are much less 
likely to be mistaken in determining the 
time between two events, which follow 
each other at a small interval, than in 
observing the precise time of the happen- 
ing of some single event" (Arts. 9093). 
By way of example, the author, making 
use of his three indications of origin, 
computed that the focus of the Lisbon 
earthquake lay under the Atlantic Ocean, 
c. 33 



at the distance of a degree of a great 
circle from Lisbon, and a degree and 
a half from Oporto. 

With singular prescience he believed 
that probably earthquakes are not of 
comparatively deep-seated origin a con- 
clusion which is now generally held by 
seismologists. He was well aware that 
data were then wanting on which to base 
any satisfactory estimate as to the depth 
of the focus, which might vary con- 
siderably, but he thought that " some 
kind of guess might be formed concerning 
it." Hazarding what he called "a ran- 
dom guess," he believed that the depth 
at which the impulse of the Lisbon 
earthquake started, " could not be much 
less than a mile or a mile and a half, and 
probably did not exceed three miles." 

In considering the merit of Michell's 
Earthquake paper as a contribution to 
science we must remember that he him- 
self modestly offered it as pretending to 
be no more than " conjectures." That so 
34 



many of his "conjectures" and "guesses" 
have been confirmed in later stages of the 
progress of science is a striking proof of 
his rare genius. He accepted the current 
doctrine of the day regarding the existence 
and nature of " subterraneous fires." 
That doctrine has long been exploded. 
The general high temperature of the 
deeper parts of the earth's crust has been 
proved by abundant evidence, though the 
problem of the cause of this internal heat 
cannot yet be regarded as solved. 

It seems not improbable that some of 
the earthquakes in volcanic regions may 
be produced, as Michell suggested, by 
the sudden descent of quantities of sur- 
face water upon the molten magma below. 
Extinct craters are apt to become lakes or 
tarns by gathering into their basins the 
results of the atmospheric precipitation 
of moisture. The sudden collapse of the 
floor of one of these craters, filled in this 
way, and the descent of a large body of 
water upon molten lava below would 

35 



conceivably give rise to a minor earth- 
quake. Michell therefore suggested what 
may be a vera causa in volcanic areas. 

Although his conjecture that the travel- 
ling of the earthquake waves along the 
surface of the earth is due to the propul- 
sion of concomitant waves of vapour 
between the strata underneath, has never 
been accepted, we should remember that 
it included the first recognition or at least 
premonitory suggestion of the potency of 
highly heated aqueous vapour as a sub- 
terranean dynamical agency in geological 
operations. Whether, if suddenly gene- 
rated at a local centre, in the manner he sup- 
posed, superheated steam could force its 
way between the strata for some distance, 
as he imagined, may be doubted. But 
since his time, and in a manner never 
dreamt of by Michell, aqueous vapour has 
been ascertained to play a stupendous part 
in volcanic activity. We now know that 
the internal magma which underlies vol- 
canic regions contains a vast volume of 
36 



aqueous and other vapours which are held 
absorbed or dissolved in its molten mass 
under the immense pressure that pre- 
vails deep below the surface. When this 
pressure is lessened as the lava mounts 
in the throat of a vent, the imprisoned 
vapours escape with explosive violence, 
blowing the liquid material into the 
finest dust, which may fill the air and 
darken the sky over a wide stretch of 
country, while at the same time the still 
steaming lava may issue incopiousstreams 
from the crater. Moreover, geologists 
have long been familiar with the fact that 
besides being erupted at the surface by 
the enormous expansive force of these 
absorbed vapours, the magma has in 
many places forced its way horizontally 
through the terrestrial crust, often be- 
tween the planes of stratification, over 
wide areas and for long distances. The 
Intrusive Sheets or Sills, so abundant in 
the British Isles, dating from Archaean 
time up to that of the Tertiary basalt- 

37 



plateaux, are stupendous monuments of 
the part which the propulsive force of 
the vapours in the subterranean magma 
has played in the past history of the 
globe. The most noted of them, the great 
Whin-Sill of the north of England, 
averages from 80 to 100 feet in thickness 
and has been injected, possibly at successive 
intervals, between and across the Car- 
boniferous strata, over an area of probably 
not less than 1000 square miles. With 
what type of earthquake the extravasation 
of such great sheets of molten material 
would be accompanied may be left to the 
imagination. 

It is remarkable that John Michell, 
who recognised the influence of elastic 
compression in generating the vibratory 
movement in an earthquake, should not 
have advanced still farther, and have per- 
ceived that the explosive shock to which 
he attributed the earthquake must of 
itself give rise to a wave of elastic com- 
pression in the earth, which starting out 
38 



in all directions may travel thousands of 
miles before becoming so feeble as to be 
no longer sensible to ordinary observation. 

n. The Structure of the Stratified Part 
of the Earth's Crust 

The most important part of Michell's 
Earthquake paper, considered as a land- 
mark in the history of geological science, 
is the account which it contains of what 
is now known as "the crust of the Earth." 
Earlier in the century John Strachey 1 
had shown that in the south-west of Eng- 
land the materials of the visible part of 
the earth had not been promiscuously 
accumulated, but had been laid down in 
a recognisable succession which he traced 
in due order from the Coal up to the Chalk. 
He further perceived that while the coal 
strata are all more or less inclined, their 
upturned edges are overlain by the Red 
Marl and later formations in horizontal 

1 Phil. Tram. vol. 30 (1719), p. 968; vol. 31 

(1 7*5), P- 395- 

- 

39 



beds. Michell's observations, which were 
all made previous to 1760, when his paper 
appeared, carried the subject considerably 
further. It must be remembered that the 
importance of organic remains in strati- 
graphy was still unknown. Indeed, there 
were probably naturalists still surviving 
who, if they did not regard these remains 
as "sports of nature," firmly believed 
them to be memorials of Noah's Flood, 
during which the whole vast thickness 
of stratified formations was supposed to 
have been deposited. Even such a shrewd 
observer as John Woodward, founder of 
the Chair of Geology at Cambridge, enter- 
tained this belief, and thought that the 
fossils had arranged themselves according 
to their weight, the heavier shells and 
bones sinking into the deeper parts of the 
sediments in the diluvial waters, while 
the lighter organisms settled down in the 
upper layers. 

Over the whole of the region in the 
south of England which he was able 
40 



personally to examine Michell found that 
the rocks everywhere displayed a striking 
order and regularity. The earth, he wrote, 
"is not composed of heaps of matter 
casually thrown together, but of regular 
and uniform strata. These strata, though 
they frequently do not exceed a few feet, 
or perhaps a few inches, in thickness, yet 
often extend in length and breadth for 
many miles, and this without varying 
their thickness considerably. The same 
stratum also preserves a uniform character 
throughout, though the strata imme- 
diately next to each other are very often 
totally different. Thus, for instance, we 
shall have, perhaps, a stratum of potter's 
clay ; above that a stratum of coal ; then 
another stratum of some kind of clay ; 
next a sharp grit-sandstone ; then clay 
again ; and coal again above that ; and 
it frequently happens that none of these 
exceeds a few yards in thickness. There 
are, however, many instances, in which 
the same kind of matter is extended to 



the depth of some hundreds of yards ; 
but in all these, a very few only excepted, 
the whole of each is not one continued 
mass, but is again subdivided into a great 
number of thin laminae, that seldom are 
more than one, two or three feet thick, 
and frequently not so much " (Art. 38). 
This careful observer next describes 
with minute precision the system of per- 
pendicular fissures (or what are known as 
joints) by which the stratified rocks are 
so abundantly traversed. He notices the 
frequent bent position of the strata, and 
shows that their inclination increases as 
they are traced towards the mountains, 
which are generally, if not always, formed 
out of the lower, and therefore older rocks. 
He illustrates the subject by the follow- 
ing experiment. "Let a number of 
leaves of paper, of several different sorts 
or colours, be pasted upon one another : 
then bending them up together into a 
ridge in the middle, conceive them to be 
reduced again to a level surface by a plane 
42 



so passing through them, as to cut off all 
the part that had been raised ; let the 
middle now be again raised a little, and 
this will be a good general representation 
of most, if not of all mountainous coun- 
tries together with the parts adjacent, 
throughout the whole world " (Art. 43). 

This simple but ingeniously contrived 
model indicates how clearly its author 
had grasped some of the main facts which 
modern geology has brought to light. 
Thus he recognised that the sequence of 
stratified formations has occasionally been 
interrupted by upheavals whereby, along 
certain lines of elevation, these formations 
have been exposed to the action of the 
various denuding forces of nature by 
which, if the denudation continued long 
enough, the upraised tract would be re- 
duced approximately to a plane, on which 
any subsequent deposits would, in modern 
phrase, lie unconformably. 

From this arrangement of the stratified 
part of the earth's crust, as he points out, 

43 



" we ought to meet with the same kinds 
of earths, stones and minerals, appearing 
at the surface in long narrow slips, and 
lying parallel to the greatest rise of any 
long ridges of mountains ; and so in fact 
we find them." He remarks that in Great 
Britain, the main trend of the outcrops 
runs nearly north by east and south by 
west. He notes also that in the course of 
the earth-movements to which the terres- 
trial crust is subject, the strata have not 
escaped rupture. " The whole set of 
strata on one side of a cleft are sunk down 
below the level of the corresponding 
strata on the other side," and he saga- 
ciously adds that, " if in some cases this 
difference in the level of the strata on the 
different sides of the cleft should be very 
considerable, it may have a great effect 
in producing some of the singularities of 
particular earthquakes" (Arts. 44, 50). 

It should be remembered that all the 
geological observations by John Michell 
referred to in the foregoing pages were 
44 



made by him during his residence at 
Cambridge ; therefore before the spring 
of the year 1 760 when his Earthquake 
paper was presented to the Royal Society. 
He never published any further contri- 
butions to geology. It has not unnaturally 
been inferred that he abandoned that 
branch of science, in order to devote him- 
self to the severer studies of which the 
fruits were given in his subsequent papers. 
But the truth is that his interest in geo- 
logical questions remained unabated to 
the end. Proof of this continued zeal is to 
be found in a long letter of the year 1788, 
hitherto unpublished, written by Michell 
to Henry Cavendish, which has fortu- 
nately been preserved among the papers 
of that great philosopher. It vividly in- 
dicates how keenly its writer, in his 
journeys to and from London, kept him- 
self on the watch for any fresh pit, 
quarry or other exposure of the rocks 
below the surface. 

It appears that Cavendish, for some 

45 



years between 1783 and 1793, was in 
the habit of making excursions with 
Dr Charles Blagden, for the purpose of 
tracing the succession and distribution of 
the strata that underlie the southern 
counties of England. Of these "Jour- 
neys," as he called them, he made notes, 
which have been preserved. The Caven- 
dish MSSl, at the instance of the Cam- 
bridge University Press, have been placed 
by the Duke of Devonshire in the hands 
of Sir T. Edward Thorpe, with a view 
to the publication of the chemical papers 
which they include. The collection of 
manuscripts contains the letter from 
Michell, together with the draft of 
Cavendish's reply. This correspondence, 
which throws an interesting light on the 
condition of geological science in this 
country during the last quarter of the 
eighteenth century, is now published for 
the first time 1 . 

1 Dr (afterwards Sir) Charles Blagden, who be- 
came one of the Secretaries of the Royal Society in 



Michell to the Hon. Henry Cavendish 

[I4TH AUGUST, IjSS] 

Dear Sir 

Some observations, as I returned 
from London, having occur'd to me 
with regard to the Northamptonshire, 
Lincolnshire, &c. yellow limestone (viz 
Dr Blagden's, not my yellow limestone) 
I take the liberty of communicating them 
to you, though perhaps hardly worth 
your attention. I could, indeed, have 
wished, I had been able to give them 
you with more precision. I lodged one 
night, in my road, at the Royal Oak, 
a new house built on Greetham Common, 

1784, appears to have acted as assistant or secretarial 
friend to Cavendish, who settled an annuity upon 
him and left him a handsome legacy. The MS. 
of the Journeys contains the joint observations made 
by the two coadjutors. It will be seen from Michell's 
letter that he was able to set them right on at least 
one important point, and that Cavendish acknow- 
ledged the correction in his reply. As already men- 
tioned, Michell's letter has been alluded to in 
Wilson's Life of Cavendish^ pp. 129, 177. 

47 



about 7 or 8 years ago, 96 miles from 
London, which is in the midst of that 
set of strata, which constitute the Yellow 
Limestone l . When walking in the garden 
there, I unexpectedly found it to be upon 
clay 2 , and enquiring of the master of the 
house about it, I found that he had been 
obliged to sink a ditch, between three 
and four feet deep, at one side of his 
garden, as well as to make two or three 
drains of about the same depth to carry 
the water into it, in order to prevent it 
from being so swampy as to be unfit for 
that purpose ; and the water at that time 
stood some inches deep in some parts of 
the ditch, though it was in the most 
droughty part of that time when every- 
thing about London was so much burnt 
up, which was also the case in a good 

1 [Apparently a name for the limestones of the 
Lower Oolite group.] 

2 [There can be little doubt that this was a 
portion of the " chalky boulder-clay " of the district, 
lying unconformably upon the various Jurassic rocks, 
and enclosing flints, bits of coal and many other 
materials from northern sources.] 



measure, though not quite so much so, 
about Greetham. I the less expected 
to find things in this state, the land 
hereabout not being low, and having 
a moderate declivity, sufficient, I should 
have thought, if it had not been retained 
by the clayey ness of the soil, to have 
carried off the water even of a wet season. 
I also observed lying about two or 
three small heaps of pebbles, among which 
were some flints ; and enquiring of the 
master of the house, whence they came, 
he informed me that they were pick'd 
up from the plough'd fields, which con- 
sisted of the same clay with the garden : 
they were lodged, as I understood, 
amongst the clay, being found here and 
there in digging into it. It was not until 
after you and Dr Blagden mention'd your 
having seen some specimens of chert, at 
some place on the coast, I think, amongst 
this set of strata, that I was aware that 
any flints were ever found belonging 
to them, and the flints I met with at 
c. . 49 



Grectham Common, must, I suppose, be 
of the same kind with those you con- 
sider'd as chert, though I should rather 
consider them as flints ; for though they 
are opake and had nothing of that horny 
look, when broken, that the flints from 
the chalky countries have, yet they have 
more of the glassy texture, and want 
that appearance of toughness, which the 
cherts in general have, so that I should 
not hesitate to call them flints rather than 
cherts. At the same time, I can easily 
conceive that our ideas of them may not 
so far coincide, but that you might well 
enough look on them as belonging to the 
cherts. I however met with, amongst 
the rest, two or three flints that every- 
body must look on as such, being, when 
broken, black and horny, and as perfect 
as the most perfect of the chalk country 
flints ; they were also roundish like those, 
and were cover'd with a dark brown 
coat ; whereas the others had no coat, 
nor any appearance of ever having had 
50 



one, that I could see, being rather angular 
and somewhat irregularly shaped. 

My landlord also told me, he had been 
informed (for he had only kept the Inn 
a year or two himself) that, when the 
house was built, they had sunk a Well 
nine yards deep through this bed of clay, 
before they came to the stone ; the clay 
may therefore, when compleat, very 
possibly have been of still greater thick- 
ness, but I had no opportunity of learning 
any further particulars about it. My 
Landlord also informed me, that he had 
been told that in sinking the above Well, 
they had met with in the clay a few 
small stragling bits of coal, but nothing, 
as far as he could make out, from the 
vague account he had been able to pro- 
cure, and which came through three or 
four hands, that seem'd to have any ten- 
dency towards a regular stratum. This 
story, however, seems to have induced 
the owner of the estate (Lord Winchelsea, 
I think), to try for coal somewhere there- 

5' 



abouts ; for he had had people to bore in 
search of it, and they had gone to the 
depth of 130 yards without any success, 
as I could easily conceive. 

This clay did not seem to compose a 
very uniform stratum, not only consisting 
of harder and softer parts, but having 
likewise those flints and pebbles scatter'd 
through it, in such manner, if I conceived 
rightly of the matter, as to shew that 
though they might perhaps have been 
formed in it originally, yet supposing 
this to be the case, they must, however, 
have been somewhat disturbed from their 
places after their formation, though I 
neither saw nor could learn circumstances 
sufficient to form any probable guess con- 
cerning the way in which these flints, as 
well as the other pebbles, which seem'd 
to contain sand and iron in their com- 
position, were formed. May I not how- 
ever, consider the circumstances and 



company in which they are found as 
rather tending to strengthen my con- 

52 



jecture concerning the origin of flints in 
general 1 ? 

Besides this bed of clay, of the existence 
of which I was not aware before my last 
return from town, there is another pretty 
considerable bed of clay (for I think it is 
not the same appearing again at another 
place) which I have often taken notice 
of, that shows itself in the side of the 
hill immediately descending towards 
Grantham, on the east side of it 2 . What 
is the thickness of this bed I don't know, 
but from what I have been able to learn 
concerning it, I should suppose it is not 
less than the other. There are also found 
in it, in one part of the stratum, some 
Cornua ammonis^ and in another part some 
selenites ; but these last I pay no great 
regard to, as they are frequently of a very 

1 [It would have been interesting to know what 
this conjecture was. How great would have been 
A lie he IPs astonishment could it then have been 
revealed to him what is now known about the history 
of the Boulder-clay which he here describes so 
minutely.] 

1 [Probably one of the clays of the Upper Lias.] 

53 



modern origin, being commonly found 
in clay, where some vitriolic water oozes 
or trickles out, provided there is a little 
calcareous matter likewise for it to unite 
with. There are a great many Bricks and 
Tiles made out of this clay for the use of 
the town of Grantham ; and I imagine, 
what might otherwise be very well, 
I think, supposed to be the case, that it 
is not an accidental mass of clay in that 
place only \ but part of a stratum of some 
extent, for I observed some other Brick- 
kilns, at a mile or two distance, on the 
side of a hill, at about the same level. 
Whether there may not be still more 
beds of clay in some other parts of this 
set of strata, I don't know, though from 
these instances and general analogy, it is 
not very unlikely there should. Almost 
immediately to the westward on this side 
Grantham 2 , we again have clay, which is 

1 [Like the tract of Boulder-clay above de- 
scribed.] 

8 [The rock formations to the west of Grantham 

54 



continued to the top of Gunnerby Hill, 
but which, however, must no doubt con- 
sist in great part of some kind of stone ; 
for it could not otherwise rise so much 
as it does in so short a space, viz 70 or 
80 yards perpendicular, I apprehend, in 
the distance of a little more than a mile. 
There is likewise another set of strata 
which form another ridge of lower hills, 
three or four miles nearer this way, about 
Foston ; all these probably contain several 
beds of clay and under these are found the 
Lyas, which consists of a great many 
alternate beds of clay and blue limestone. 
I believe I have formerly mentioned 
it to yourself and Dr Blagden, but not 
recollecting whether I have before insisted 
so much upon it, as I might have done, 
I shall take this opportunity, which the 
country I have just been mentioning 
suggests, of observing, that to the west- 
ward of all that edge of Dr Blagden's 
yellow limestone, next our side of the 

consist of what are now known as the Upper, Middle 
and Lower Lias.] 

55 



sets of strata which run from north to 
south through the island of Great Britain, 
as far as I am acquainted with them, lies 
the Lyas at no very great distance ; 
though, indeed, with two or three sets 
of strata, viz those of Gunnerby and 
Foston, between them ; these run into 
Leicestershire to the south, and to where 
the Trent falls into the Humber, and the 
upper part of the Humber to the north, 
the Lyas being the lowest of all these 
sets of strata, and all of them lying below 
the yellow limestone 1 in order, but 
nowhere having any coal near them ; 
whereas our yellow limestone 2 has no 
Lyas anywhere under it or near it to the 
westward of it, but on the contrary, 
everywhere coal very near the western 
edge of it, all the way from Leicestershire 
by the edge of Nottinghamshire and 
Derbyshire, and a long way into York- 

1 [Now known as the group of Lower Oolites.] 

1 [That is, the Magnesian Limestone of the 

Permian system which stretches as a broad band 

from near Nottingham to the mouth of the Tyne, 

a distance of 1 50 miles.] 

56 



shire, and how much further I don't for 
certain know ; and in many places, if not 
everywhere, the coal is found under our 
yellow limestone, through which they 
sink in many places in order to come at it. 
Since I began to write this letter I 
received from M r Beatson of Rotheram, 
a parcel of the substance he was mention- 
ing to you. He sent, by the person who 
brought it to me, an apology for not 
having sent it before, and saying at the 
same time that it was not yet so good 
a specimen as he had wished to have sent. 
As it was directed to me, though it ought 
perhaps rather to be considered as your 
property, I have taken the liberty of 
reserving the half of it for myself, which, 
however, if you want any more than 
I have sent you, either to make experi- 
ments upon, or for any other purpose, 
I will send you whenever you please. It 
seems to be in general a good deal harder 
than the black lead used for pencils, 
though some of the thin flakes seem to 
mark pretty well ; probably the difference 

57 



may be owing to too large a quantity of 
Iron contained in it ; for it appears by it's 
applying so very strongly as it does to 
the magnet, to contain a great proportion 
of that metal. 

With best respects to yourself and due 
comp s to all friends when you see them, 
particularly those of the " Crown and 
Anchor" and "Cat and Bagpipes" clubs 1 , 
I am, Dear Sir 

Your obed' humble servant 2 

J. MICHELL 

THORNHILL, 14 Aug 1788 

1 The Crown and Anchor Tavern, Strand, as 
already mentioned, was the meeting place of the 
Royal Society Club at this time and continued to 
be so for sixty-eight years, from 1780 to 1848. 
Reference has been made (p. 20) to MichelPs frequent 
appearance at the Club, where he constantly met 
Cavendish. The "Cat and Bagpipes" was "a 
public house of considerable notoriety, with this 
sign. It existed at the corner of Downing Street, next 
to King's Street. It was also used as a chop-house, 
and frequented by many of those connected with the 
public offices in the neighbourhood " (Notes and 
Queries, Nov. 9, 1850, p. 397). But nothing seems 
to be known of the Club to which Michell refers 
as meeting there. 

* This deferential expression, so characteristic 

58 



Along with this letter therehas been pre- 
served among the Cavendish papers the 
rough draft of the reply to it sent by the 
philosopher, which is chiefly interesting 
as an example of the detailed examination 
which Henry Cavendish continued for 
some years to bestow upon the sequence 
and distribution of the geological forma- 
tions of the southern half of England. 
With only lithological characters as a 
guide, he could hardly fail to make 
mistakes in the order of superposition. 

" I am obliged to you and M r Beatson 
for the plumbago and to you for your 
letter. 

I have got some which I received from 
Wales, part of which, I think, is purer 
than M r Beatson's. But the rest consists 
of flakes of a more sparkling nature than 
Beatson's and less disposed to mark paper. 
I have also some which I received under 

of the period, was the usual manner in which Michell 
ended his letters to Cavendish. It is found in the 
original of his paper of 26th May 1783, which is 
printed in Phil. Tram. vol. 74 (1784), p. 35. 

59 



the name of sulphur-iron, and which is 
much the same to appearance as the latter 
part of the Welsh specimen. I analysed 
this and found it to contain more siliceous 
earth than plumbago, besides a good deal 
of iron, not so much in the state of plum- 
bago but what it would dissolve in acids. 

I suppose it must be the yellow lime- 
stone about Bridport in which Dr Bl. 
told you we found chert. How far it de- 
serves that name I can not say, but to 
the best of my remembrance it was of a 
much coarser grain, and had not at all the 
appearance of flint ; but my memory is 
too imperfect for me to attempt to de- 
scribe it to you. As the circumstances 
relating to it are rather remarkable, I will 
mention what we saw of it last year. 

On descending the chalk hills between 
Dorchester and Bridport, by the time 
we got about ^ way to the bottom, we 
came to the yellow limestone, which 
seemed separated from the Chalk only by 
a stratum of clay of no great thickness. 
60 



A few miles farther, the stone, though to 
appearance much the same, was found to 
be of a siliceous nature, with very little 
calcareous matter in it. At Lyme the cliffs 
are blue clay and blue Lyas ; but the top 
of the hill, which we pass over imme- 
diately before we come to Lyme, consists 
of gravel composed of this chert ; and 
about a mile to the west of Lyme was a 
hill with a steep bank towards the sea, 
the foot of which was blue Lyas with 
yellow limestone over it, mixed with 
veins of this chert, so much like limestone 
that one could hardly distinguish them 
by the eye ; but it must be observed that 
this, as well as most of the limestone we 
saw, is of a hard compact and rather brown 
kind. 

From hence to Sidmouth the soil con- 
sisted chiefly of this cherty gravel, but the 
cliffs on each side of Sidmouth consisted 
of red rock (the sandy kind consisting of 
thick strata) ; only on the east side they 
were covered with a great thickness of 

61 



the same chert-gravel as the hill by Lyme. 
From hence we had red rock and red soil, 
without any chert-gravel to Halldown 
[Haldon], which is a hill extending from 
a little to the west of Exeter to near 
Teignmouth. The upper part of this hill 
consisted of the above-mentioned chert- 
gravel, so that it appears that the lime- 
stone of this country is very much mixed 
with chert, a great deal of which seems 
to have been reduced to gravel and de- 
posited on strata of older formation, at a 
great distance from the limestone where 
it was formed. Besides, Halldown, the 
top of which is covered with this matter, 
is, I believe, entirely separated from the 
rest of the country by a broad tract of the 
red-rock country. In the cliffs between 
Minehead and Watchett, I saw the red- 
rock lying immediately under the blue 
Lyas. 

In digging the tunnel for the canal in 
Gloucestershire, they have found one or 
more beds of clay between the strata of 

62 



yellow limestone, and I believe the Chalk 
is not free from them. A little to the 
west of D unstable considerable springs 
of water break out on the N.W. side 
of the Chalk hills, about the level of Dun- 
stable. 

I believe you must be right in sup- 
posing your yellow limestone to be quite 
distinct from the other. From what I 
can learn, I believe the N.W. edge of 
the other, after running from Gunnerby 
Hill on the E. side of the Trent, crosses 
the H umber and runs under the Yorkshire 
Chalk, and appears again about Castle 
Howard, and so runs to Scarborough, the 
Chalk in that place lapping over and ex- 
tending further west than the limestone 1 ." 

This letter furnishes an example of the 
detailed manner in which Cavendish con- 
ducted his "Journeys." It contains several 

1 The last page and a half of this draft-letter 
consists of an account of a journey made by Dr 
Blagden from Dieppe to Paris, with details of his 
observations on the geological features of the region 
through which he passed. 

63 






interesting original observations. Of 
these the most remarkable is that which 
recognised the important overlap of the 
Cretaceous series of Yorkshire whereby 
almost the whole of the underlying 
Jurassic formations are concealed for a 
space of some twenty miles a feature in 
the geological structure of the country 
of which the full import was not under- 
stood for many years after his time. He 
evidently accepted Michell's opinion that 
the yellow limestone which immediately 
overlies the Coal-measures of Derbyshire 
and Yorkshire could not be the same as 
that which overlies the Lias, but must 
belong to a lower platform in the suc- 
cession of formations. 

In the course of years, with his eyes 
constantly on the alert for fresh light on 
geological questions, Michell made many 
original observations that well deserved to 
be published, but with characteristic 
modesty he refrained from putting them 
in print. At the same time, as in his 

64 



correspondence with Priestley and with 
Cavendish, he was ready to communicate 
them to any enquirer who took an interest 
in the subject. By a happy accident one 
of these communications to a friend, was 
committed by this friend to writing and 
was published seventeen years after 
Michell had passed away. In August 
1 8 1 o there appeared, in the Philosophical 
Magazine, a letter from John Farey, Sen., 
a well-known geologist of the day, enclos- 
ing certain notes made by John Smeaton, 
the eminent engineer, and endorsed by 
him as " Mr Michell's account of the 
south of England strata." Farey states 
that this account was probably made 
verbally by Michell to his friend Smeaton, 
very soon after November 1788, and was 
taken down by Smeaton " on the cover 
of a recent letter as being the only piece 
of paper then at hand ; for Mr Smeaton 's 
decease in 1792 shows that it must have 
been prior to that time/' The document 
was as follows : 

G. 65 



Yards 

Chalk 120 

Golt 50 

Sand, of Bedfordshire 10 or 20 

Northampton lime and Port- 
land limes lying in several 
strata 100 

Lyas strata 70 or 100 

Sand, of Newark about 30 

Red ClayofTuxford 100 

Sherewood Forest, pebbles and 

gravel 50 unequal 

Yery fine white sand uncertain 

Roch Abbey and Brotherton 

limes 100 

Coal strata of Yorkshire l ... 

Farey, in communicating this Table, 
remarked that the " account of the strata 
imperfect as it is, shews that Mr Michell 
was acquainted with the principal features 
of the south of England strata, at an 
earlier period than anything that has been 
published on the subject." He adds as 

1 The Northampton limestone belongs to the 
Inferior Oolites, and the Portland limestone to the 
Upper Oolites ; they both lie above the Lias as shown 
in the Table. The Keuper and Bunter divisions 
of the Trias are here correctly placed between the 
Lias and the Permian Magnesian Limestone. 

66 



specially remarkable that Michell should 
have correctly applied to the strata be- 
tween Grantham and Balderton the ap- 
pellation of Lyas, a term not then known 
or in use nearer than Gloucestershire or 
Somersetshire, showing that this saga- 
cious observer " had contemplated the 
identity of the British strata over wide 
spaces." 

Few men, unless they chance to be ex- 
perienced field-geologists, can fully appre- 
ciate the amount of time, skill and labour 
which the construction of this Table of 
Strata required. It must represent the 
result of the journeys of many years over 
a large part of the southern half of Eng- 
land. It implies an infinite patience and 
no little lithological deftness in correlat- 
ing the petrographical characters of the 
various strata, with such success as to be 
able to identify the different members at 
distant parts of their outcrop. The key 
furnished by organic remains to the 
chronological sequence of the formations 

67 



had not yet been discovered by William 
Smith, who, born two years after MichelFs 
transference to Thornhill, did not begin 
to publish his epoch-making discovery 
until the distinguished Rector had passed 
away. That the Table given above should 
be imperfect and in some particulars in- 
accurate does not derogate from the 
author's credit and originality. He un- 
questionably established the succession of 
the main subdivisions of the English 
Mesozoic formations, and he did this by 
laborious determinations of the order of 
superposition and the identity or close 
resemblance of mineral characters over a 
wide region, without any help from pa- 
laeontological evidence. 

Though students of the history of 
geological discovery in England have 
been acquainted with MichelTs work and 
have sometimes expressed their high 
sense of its value, there is reason to think 
that the pioneer merit of his contributions 
to geology has never yet been adequately 
68 



recognised. Lyell indeed has referred to 
his "original and philosophical" views 
on earthquake phenomena and has de- 
clared that "some of his observations 
anticipated in so remarkable a manner the 
theories established forty years afterwards, 
that his writings would probably have 
formed an era in the science, if his re- 
searches had been uninterrupted. He 
held, however, his professorship only 
eight years 1 , when hiscareer was suddenly 
cut short by preferment to a benefice. 
From that time he appears to have been 
engaged in his clerical duties, and to have 
entirely discontinued his scientific pur- 
suits, exemplifying the working of a 
system still in force at Oxford and Cam- 
bridge, where the chairs of mathematics, 
natural philosophy, chemistry, botany, 
astronomy, geology, mineralogy and 
others, being frequently filled by clergy- 
men, the reward of success disqualifies 

1 His tenure of the office, as already shown, was 
ess than two years. 

6 9 



them, if they conscientiously discharge 
their new duties, from further advancing 
the cause of science, and that, too, at the 
moment when their labours would natur- 
ally bear the richest fruits 1 ." 

The statement in this quotation that 
from the time of his entering upon his 
clerical duties, Michell " appears to have 
entirely discontinued his scientific pur- 
suits " was doubtless based on the fact 
that after the appearance of his Earth- 
quake paper he never published any fur- 
ther contribution to geological science. 
We may well believe that his clerical 
duties were always conscientiously and 
zealously discharged. But up till near the 
close of his life he never ceased to pursue 
his scientific studies. In regard to his 
geological proclivities we have seen that 
so far from abandoning that subject he 

1 LyelPs Principles of Geology^ Tenth Ed. vol. i, 
p. 61. To this testimony should be added that of 
Fitton, Phil. Mag. 1832, I, p. 268: K. A. von Zittel, 
Geschichte der Geologie (1899), pp. 8l, 157. Michell 
is included in the author's Founders of Geology^ 1897. 

70 



continued to prosecute it with a breadth, 
originality and success which show him 
to have been the most accomplished Eng- 
lish geologist of his time. He was in no 
hurry to publish his observations though 
ever willing to communicate them to his 
friends, and they have come to light al- 
most by accident since his death. He 
well deserves to be ranked as one of the 
founders of Geology in England. 

But his "scientific activities, extending 
beyond the geological sphere, ranged 
far and wide through the physical 
sciences, and his leisure hours at Thorn- 
hill were largely devoted to personal 
research and experiment in that wide 
domain. Probably a good deal of his 
original work was never published, but 
his papers, which found an appropriate 
place in the Philosophical Transactions \ 
have given him a title to high rank among 
the natural philosophers of the eighteenth 
century. To the consideration of this side 
of his achievement I shall now turn. 



II 

CONTRIBUTIONS TO PHYSICS 

IT was in the realm of Physics that 
the originality and brilliance of John 
Michell's mind found their widest scope. 
A living writer has recently said : "In 
the entire century which elapsed between 
the death of Newton and the scientific 
activity of Green, the only natural philo- 
sopher of distinction who lived and taught 
at Cambridge was Michell ; and for some 
reason which, at this distance of time, it 
is difficult to understand fully, Michell's 
researches seem to have attracted little or 
no attention among his collegiate con- 
temporaries and successors, who silently 
acquiesced when his discoveries were 
attributed to others, and allowed his 
name to perish entirely from Cambridge 
tradition 1 ." There can at least be no 

1 A History of the Theories of Aether and Electricity ', 
by Professor E. T. Whittaker, F.R.S., 1910, p. 167. 

7 2 



doubt that in his lifetime Michell en- 
joyed the esteem and respect of the most 
eminent men of science in his day. 
His distinction as an investigator was 
promptly recognised, as we have seen, 
by his early election into the Royal 
Society, when Henry Cavendish and 
other men of note became his friends and 
correspondents. But it was not until after 
he left Cambridge that his eminence in 
natural philosophy was displayed in the 
successive papers which he communicated 
to the Philosophical Transactions. 

The consideration of his researches in 
physical science may be grouped under 
the heads of (A) Magnetism, (B) Vision, 
Light, etc., (C) The Density of the Earth. 
A separate section will be devoted to his 
investigations in Astronomy. 

A. Magnetism 

In Michell's first published essay in 
science the little volume on Artificial 
Magnets two of his prominent charac- 

73 



tcristics were conspicuously shown, 
originality and modesty. Though from 
the title of the book it might be supposed 
to be merely a new method of producing 
artificial magnets, it yet contained some 
fresh researches in magnetism including 
the discovery of the law of attraction 
which is " the basis of the mathematical 
theory of Magnetism 1 /' The author 
believed his method of making artificial 
magnets to be a contrivance of his own, 
but he admitted that it might prove to be 
the same as that of his eminent contem- 
porary Dr Gowin Knight. But of much 
more importance than the originality of 

1 Whittaker, History of Theories of Aether and 
Electricity^ p. 55. The full title-page of MichelFs 
work is as follows: u A Treatise of Artificial Magr 
nets; in which is shewn an easy and expeditious 
Method of making them, superior to the best natural 
ones, by J. Michell, B. A. Fellow of Queens' College, 
Cambridge. Printed by J. Bentham, Printer to the 
University and sold by W. and J. Mount and 
T. Page on Tower Hill&c. MDCCL. (Price i/-)." 
The copy of the volume in the Library of the Royal 
Society has a MS. note at the foot of the title-page : 
"Presented March 22, 1750." 

74 



his invention was the light which he was 
able to throw on the laws of magnetism. 
Thus he found that according to his 
observations " the magnetical attraction 
and repulsion are exactly equal to each 
other." He made and announced the 
discovery that " the attraction and re- 
pulsion of magnets decreases as the squares 
of the distances from the respective poles 
increase." Yet he modestly remarks 
that, although his own experiments made 
the conclusion very probable, "I do not 
pretend to lay it down as certain, not 
having made experiments enough yet to 
determine it with sufficient exactness 1 ." 
It will be remembered that his contri- 
bution to magnetism was one of the 
grounds set forth in the certificate for 
his election into the Royal Society, and 
that one of his sponsors was Dr Gowin 
Knight, the most noted authority of the 
day on this branch of science. 

1 Treatise of Artificial Magnet^ p. 19. 

75 





B. Vision, Light, and Colours 

Interesting proof of the range of 
Michell's studies in natural philosophy 
and of the singularly large-minded gene- 
rosity with which he freely communi- 
cated to other fellow-workers the results 
of his own unpublished researches is 
furnished by the record of his association 
with Joseph Priestley. That illustrious 
philosopher became minister of Mill Hill 
Chapel, Leeds, in 1767, the same year 
that saw John Michell settled in the 
rectory of Thornhill. He had already 
made known his growing heterodoxy, 
but he had also shown such striking 
powers in scientific discussion, particu- 
larly in regard to electricity, that the 
Royal Society had already in 1766 elected 
him one of its body. Leeds and Thorn- 
hill being only a few miles apart, it was 
natural that the two men of science 
should become acquainted with each 
other. In these days it said much for the 
76 



broad-mindedness of the Rector of Thorn- 
hill that he entered into the friendliest 
relations with the Unitarian dissenter. 
He could hardly fail to be interested in 
the publication of Priestley's volume on 
The History and Present State of Electricity 
which made its appearance in this same 
year 1767. During the lapse of a few 
years much friendly personal intercourse, 
as well as correspondence, arose between 
the two men. Priestley had then begun 
to collect material for another work on 
physical science which was published in 
1 772 *. During the five years over which 
the writing of this treatise extended, he 
frequently consulted the Rector on the 
various questions which he had to discuss, 
and he fully acknowledged the value of 
the assistance which was always willingly 
forthcoming from that source. He has 
stated that "in writing the History of the 

1 The title of this work is History and Present 
State of Discoveries relating to Vision, Light and 
Colour j, 2 vols. 4 to, 1772. 

77 



Discoveries relating to Vision* I was much 
assisted by Mr Michell, the discoverer of 
the method of making artificial magnets. 
Living at Thornhill not very far from 
Leeds, I frequently visited him, and was 
very happy in his society 1 ." 

In the two quarto volumes to which 
Priestley refers in this quotation, he ac- 
knowledges in detail his indebtedness to 
Michell. From his statements and his 
quotations from the Rector's letters we 
learn what were MichelFs views on a 
number of physical questions on which 
he does not appear ever to have himself 
published anything. Thus in reference 
to the seat of vision, Priestley remarks : 
" I shall beg leave to present to my 
readers some other arguments which 
escaped the notice of previous observers, 
but which were suggested to me by my 
friend Mr Michell 2 ." Later in the same 

1 Life cmd Correspondence of Joseph Priestley^ by 
J. T. Rutt, 1831, vol. I, p. 78. 

Op. at. vol. i, p. 198. Michell as a staunch 

78 



volume he states : " My objections to 
Newton's manner of accounting for the 
colours of thin plates are of long standing, 
but the hint of accounting for them in the 
manner that I have attempted to do [by 
the doctrine of attractions and repulsions] 
was first suggested to me by Mr Michell, 
agreeably to whose conjectures relating 
to this subject, I have given the preceding 
account of the probable cause of these 
appearances 1 ." 

Priestley likewise refers to MichelFs 
skill in devising apparatus for the purpose 
of illustrating or solving physical pro- 
blems. Thus with regard to another 
phenomenon of light he states : " Mr 
Michell some years ago endeavoured to 
ascertain the momentum of light in a 
much more accurate manner than those 
in which M. Homberg and M. Mairan 
had attempted it ; and though his appa- 

fol lower of Newton believed in the corpuscular 
theory of light. 
1 Vol. I, p. 311. 

79 



ratus was disordered by the experiment, 
and on other accounts, he did not pursue 
it so far as he had intended, it was not 
wholly without success ; and the con- 
clusions that may be drawn from it are 
curious and important 1 ." 

After describing the apparatus which 
had been employed, Priestley proceeds 
to show that the conclusions which its 
contriver was disposed to draw from his 
observations, as far as they had gone, 
pointed to the " mutual penetrability of 
matter." He states that the ingenious 
hypothesis of Boscovich on this subject, 
" or at least one that is the same in every- 
thing essential, occurred also to my friend 
Mr Michell, in a very early period of 
his life, without his having had any 
communication with M. Boscovich, or 
even knowing that there was such a 
person. These two philosophers had 
even hit upon the same instances, to 
confirm and illustrate their hypotheses, 

1 Op. clt. p. 387. 
80 



especially those relating to contact, light 
and colours. 

" This scheme of the immateriality of 
matter, as it may be called, or rather, the 
mutual penetration of matter, first occurred 
to Mr Michell on reading Baxter On the 
Immateriality of tlie Soul. He found that 
this author's idea of matter was, that it 
consisted, as it were, of bricks, cemented 
together by aq immaterial mortar. These 
bricks, if he would be consistent to his 
own reasoning, were again composed of 
less bricks, cemented, likewise, by an 
immaterial mortar and so on ad infantum. 
This putting Mr Michell upon the con- 
sideration of the several appearances of 
nature, he began to perceive that the 
bricks were so covered with this im- 
material mortar, that if they had any 
existence at all, it could not possibly be 
perceived, every effect being produced, at 
least in nine instances in ten certainly, 
and probably in the tenth also, by this im- 
material, spiritual and penetrable mortar. 
c. 81 






Instead, therefore, of placing the world 
upon the giant, the giant upon the 
tortoise, and the tortoise upon he could 
not tell what, he placed the world at 
once upon itself; and finding it still 
necessary, in order to solve the appear- 
ances of nature, to admit of extended 
and penetrable immaterial substance, if 
he maintained the impenetrability of 
matter ; and observing farther, that all 
we perceive by contact, etc. is this pene- 
trable immaterial substance, and not the 
impenetrable one, he began to think he 
might as well admit of penetrable material, 
as well as penetrable immaterial substance, 
especially as we know nothing more of 
the nature of substance, than that it 
is something which supports properties, 
which properties may be whatever we 
please, provided they be not inconsistent 
with each other, that is, do not imply 
the absence of each other. This by no 
means seemed to be the case in supposing 
two substances to be in the same place at 
82 



the same time, without excluding each 
other ; the objection to which is only 
derived from the resistance we meet with 
to the touch, and is a prejudice that has 
taken its rise from that circumstance, and 
is not unlike the prejudice against the 
Antipodes, derived from the constant ex- 
perience of bodies falling, as we account 
it, downwards 1 ." 

In connection with other problems 
in light and vision Priestley refers to 
information supplied to him by Michell 
and quotes from some of the philosopher's 
published astronomical papers where these 
problems are considered. 

1 Op. at. pp. 392-3. As Professor Whittaker 
has pointed out, Faraday's suggestion that "an 
ultimate atom may be nothing else than a field of 
force electric, magnetic and gravitational sur- 
rounding a point-centre, is substantially the view of 
Michell and Boscovich." History of the Theories of 
Aether and Electricity (1910), p. 217. 



C, The Density of the Earth 

The most ingenious and most im- 
portant piece of apparatus devised by 
John Michell at his Yorkshire home was 
his bold and original invention of the 
Torsion-balance with which he proposed 
to determine the mean density of the 
Earth. It was probably his last feat in 
mechanical contrivance, at least he did 
not live to put it into use. After his 
death the apparatus passed into the hands 
of Henry Cavendish who, making some 
modifications and improvements in it, 
carried out MichelFs purpose with 
brilliant success, in what has since been 
known as the " Cavendish experiment. 1 * 
In communicating his account of the 
experiment to the Royal Society 1 , Caven- 
dish, who seemed so indifferent to the 
recognition of his own scientific work, 
took care to bear his testimony to the 

1 Phil. Trans, vol. 88 (1798), p. 469. The paper 
was read to the Society on 2ist June 1798. 



originality of his deceased friend. "Many 
years ago," so he wrote, " the Rev. John 
M ichell of this Society contrived a method 
of determining the density of the earth, 
by rendering sensible the attraction of 
small quantities of matter ; but as he was 
engaged in other pursuits, he did not 
complete the apparatus till a short time 
before his death, and did not live to make 
any experiments with it. After his death 
the apparatus came to the Rev. Francis 
John Hyde Wollaston, Jacksonian Pro- 
fessor at Cambridge, who not having 
conveniences for making experiments 
with it, in the manner he could wish, 
was so good as to give it to me." 

" The apparatus is very simple : it 
consists of a wooden arm, 6 feet long, so 
as to unite great strength with little 
weight. This arm is suspended in an 
horizontal position, by a slender wire, 
40 inches long, and to each extremity is 
hung a leaden ball, about 2 inches in 
diameter, and the whole is enclosed in 



a little wooden case to defend it from 
the wind. 

"As no more force is required to make 
this arm turn round on its centre than 
what is necessary to twist the suspending 
wire, it is plain that if the wire is suffi- 
ciently slender, the most minute force, 
such as the attraction of a leaden weight 
a few inches in diameter, will be sufficient 
to draw the arm sensibly aside. The 
weights which Mr Michell intended to 
use were 8 inches in diameter. One of 
these was to be placed on one side of the 
case opposite to one of the balls, and as 
near it as could conveniently be done, and 
the other on the other side, opposite to 
the other ball, so that the attraction of 
both these weights would conspire in 
drawing the arm aside ; and, when its 
position, as affected by these weights, 
was ascertained, the weights were to be 
removed to the other side of the case, so 
as to draw the arm the contrary way, and 
the position of the arm was to be again 
86 



determined ; and consequently, half the 
difference of these positions would shew 
how much the arm was drawn aside by 
the attraction of the weights. 

" In order to determine from hence 
the density of the Earth, it is necessary 
to ascertain what force is required to draw 
the arm aside through a given space. 
This Mr Michell intended to do, by 
putting the arm'in motion, and observing 
the time of its vibrations, from which it 
may easily be computed 1 ." 

" Mr Michell had prepared two wooden 
stands on which the leaden weights were 
to be supported, and pushed forwards, 
till they came almost in contact with 
the case ; but he seems to have intended 
to move them by the hand. 

"As the force with which the balls 



1 " Mr Coulomb has, in a variety of cases, used 
a contrivance of this kind for try ing small attractions; 
but Mr Michell informed me of his intention of 
making this experiment, and of the method he in- 
tended to use, before the publication of any of 
Mr Coulomb's experiments." [Note by Cavendish .] 



are attracted by these weights is exces- 
sively minute, not more than 



their weight, it is plain that a very 
minute disturbing force will be sufficient 
to destroy the success of the experiment ; 
and from the following experiments it 
will appear, that the disturbing force 
most difficult to guard against is that 
arising from the variations of heat and 
cold ; for, if one side of the case is 
warmer than the other, the air in con- 
tact with it will be rarefied, and, in 
consequence, will ascend, while that on 
the other side will descend, and produce 
a current which will draw the arm 
sensibly aside. 

" As I was convinced of the necessity 
of guarding against this source of error, 
I resolved to place the apparatus in a room 
which should remain constantly shut, and 
to observe the motion of the arm from 
without, by means of a telescope ; and 
to suspend the leaden weights in such 
a manner, that I could move them with- 
88 



out entering the room. This difference 
in the manner of observing, rendered it 
necessary to make some alteration in 
Mr Michell's apparatus ; and as there 
were some parts of it which I thought 
not so convenient as could be wished, 
I chose to make the greatest part of it 
afresh." 

The " Cavendish experiment r has 
become famous in the annals of physical 
science. One of the most appreciative 
accounts of it and of Michell's share in 
preparing for it was penned by the dis- 
tinguished Professor of Natural Philo- 
sophy in the University of Edinburgh, 
James David Forbes, more than half a 
century after both Michelland Cavendish 
had been laid in the grave. The con- 
cluding sentences of his narrative may be 
quoted here : " Cavendish conducted the 
experiment with his usual patience, judg- 
ment and success ; he found the joint 
attraction of the small balls and large 
spheres to be about ^ of a grain, their 

89 



centres being 8-85 inches apart, and he 
thence computed the density of the 
Earth to be 5-48 times that of water. 
Cavendish's paper is, as usual, a model of 
precision, lucidity and conciseness. It 
would be difficult to mention in the 
whole range of physics a more beautiful 
and more important experiment 1 ." 

Since Cavendish improved Michell's 
apparatus and first put it to the use for 
which its designer constructed it, the 
experiment has been repeated by several 
observers with an approximately similar 
result 2 . The most recent repetition is 
that of Mr C. V. Boys. By an ingenious 
reconstruction of apparatus and availing 
himself of the great sensibility obtained 
by the use of quartz-fibres instead of 
metal wires this accomplished physicist 

1 Professor Forbes* description is contained in 
the Sixth Dissertation of the Eighth Edition of the 
Encyclopaedia Bntannlca^ p. 834. 

2 See Reich, Compt. rendus^ 1837, p. 697 ; Baily, 
Mem. Astron. Soc. vol. XIV; Phil. Mag. xxi (1842), 
p. Ill ; Cornu, Compt. rend. vol. 86, pp. 571, 699, 
1OOI. 

9 



has computed the mean density of the 
Earth to be 



III 
CONTRIBUTIONS TO ASTRONOMY 

THE studies pursued by John Michell in 
this branch of science were marked by 
his characteristic originality and insight. 
Not only was he an actual observer of 
the heavens, working with a reflecting 
telescope of his own construction, but in 
his theoretical discussion of stellar phe- 
nomena he introduced the mathematical 
computation of probabilities, and showed 
sometimes a remarkable prescience that 
seems to anticipate the discoveries of 
more recent times. Reference has already 
been made to the family tradition that 
Michell gave William Herschel his first 
lessons in Astronomy and taught him the 
art of making reflectors. Before entering 

1 Boys, "On the Newtonian Constant of Gravi- 
tation,*^//. Tram. vol. 1 86(1 896) ; seealsoPrw. Roy. 
Soc. vol. 46, p. 253 ; Proc. Roy. Imtit. vol. xiv (i 894). 

9' 



on the consideration of Michell's own 
astronomical work it maybe convenient if 
we take note of what were the actual per- 
sonal relations of these two astronomers. 
It is now clearly established that they 
started quite independently of each other 
in the actual construction and employ- 
ment of the reflecting telescope. We do 
not know when and under what con- 
ditions the Rector of Thornhill began to 
construct the large instrument which 
ultimately became the property of Her- 
schel, but it would appear that he had 
made considerable progress, if he had not 
completed it before 1781. Herschel did 
not begin to study astronomy until 
1773 when he was still actively engaged 
in the multifarious duties of his musical 
profession at Bath. In the following 
year he began to grind specula 1 . After 
six years, during which he worked la- 
boriously with his telescope, he was able 

1 The Scientific Papers of Sir William HerscM, 
vol. I, pp. xxxi-xxxii. 

92 



in the summer of 1780 to send to the 
Royal Society two papers in which the 
results of his first researches were given 1 . 
These papers revealed to \ne world the 
advent of a new astronomer of unusual 
promise. They would probably be kno\vn 
and appreciated by Michell, for they 
appeared in the Philosophical "Transactions. 
But, as already stated (p. 18), they were 
more pointedly brought to his notice by 
his friend Dr Watson, who had interested 
himself at Bath in the work of the pre- 
cocious astronomical musician. Herschel 
took advantage of the opening provided by 
Michell's letter to him of 2 ist January 
1781. To two of his letters Michell sent 
him a long reply (i2th April) dealing 
with the construction of mirrors and the 
relative merits of different types for large 
and small apertures. Only a month before 
this letter was written Herschel had made 
his great discovery of Uranus, and had 
thus leaped into a foremost place among 

1 Phil. Trans, vols. 70 and 71. 

93 



the astronomers of the world. The cor- 
respondence between him and the Rector 
of Thornhill does not appear to have been 
maintained ; but as Herschel was elected 
a Fellow of the P.oyal Society on 6th 
December 1781, the two men of science 
\vould now have opportunities of personal 
intercourse at the meetings of the Society 
and the convivial gatherings of the Royal 
Society Club. Herschel in subsequent 
years took occasion, in a paper read before 
the Royal Society, to refer appreciatively 
to the work done at Thornhill. "Mr 
Michell," he said, " has also considered 
the stars as gathered together into groups 
(Phil. Trans, vol. 57, 1767, p. 249) which 
agrees with the subdivision of our great 
system here pointed out. He founds an 
elegant proof of this on the computation 
of probabilities, and mentions the Pleiades, 
the Praesepe Cancri, and the nebula (or 
cluster of stars) in the hilt of Perseus's 
sword as instances 1 ." 

1 Phil. Trans. 75 (1785). 

94 



The only record which I have been 
able to recover of an actual meeting of 
the two astronomers was one made by 
Herschel during a tour in the year 1792 
when he passed through Thornhill and 
called at the rectory. But the Rector, 
now near the close of his life, was dis- 
abled and frail. Herschel has noted : 
"We saw Mr Michell's telescope; it is 
on an equatorial stand, being without 
cover behind. I put my hand into the 
opening and felt the face of the object 
speculum so wet as to moisten my fin- 
gers. Mr Michell was very indifferent 
in health." 

When Herschel, in the course of a 
holiday trip with his wife next year, 
spent a couple of hours at the place, 
Michell had already passed away, and 
the instruments that had gradually been 
accumulated at the rectory were about 
to be removed. He took another look at 
the collection and made a note that he 
had "bought Mr MichelTs great tele- 

95 



scope and paid Mr Turton 30 pounds 1 .'* 
It is interesting to know that the instru- 
ment was put into good order and was 
used in his subsequent researches by the 
great astronomer into whose hands it had 
come. 

We may now pass on to consider 
Michell's genius for astronomy as dis- 
played in the papers which he communi- 
cated to the Royal Society and which 
duly appeared in the Philosophical Trans- 
actions. I am glad to be able to present 
the following estimate of these papers, 
which at my request has been prepared 
for this Memoir by my friend Sir Joseph 
Larmor. 

" In designing his apparatus to measure 
the gravitational attraction of a globe of 
lead, and thence to deduce the mean 
density of the Earth, Michell was the 
pioneer in the standard method of deter- 
mining very small forces by taking advan- 
tage of the torsion produced by them 

1 Herscbirs Scientific Papers, vol. I, p. Ix. 

9 6 



in a wire. It was shortly afterwards, as 
Cavendish remarks, that Coulomb ap- 
plied the same principle, in a classical 
series of experiments, to the exact deter- 
mination of electric and magnetic attrac- 
tions : and, in various more convenient 
forms, it is now one of the main resources 
of delicate physical measurement. But 
Michell's (and. Cavendish's) mastery of 
it, and his just anticipation of its power, 
went far beyond his age ; he designed 
and constructed appliances with con- 
fidence, for a precise estimation of forces 
so minute that they could hardly even be 
detected in any other way : even nowa- 
days his application of the principle to 
gravitation demands the resources of a 
master. 

"It is to be expected that a man who 
could confidently engage in preparations 
to weigh a ball of lead against one of the 
celestial bodies would be capable of deep 
views on other astronomical questions. 
An examination of his Memoir of 1767 
c. 97 



confirms this surmise *. As regards general 
astronomical speculation on stellar sys- 
tems and their nature, it gives him a place 
alongside Huygens, Wright and Kant 2 . 
Further, in more definite fields, it credits 
him with initiation of the applicati Dn of 
mathematical methods, resting on proba- 
bility and statistics, to the celestial sys- 
tems. The quantity of material which 
had then been accumulated was far too 
small for wide statistical inferences of 
much certainty ; yet Michell amply 
demonstrated, for the first time 3 , the 



1 The title of this paper is as follows : " An 
inquiry into the probable Parallax and Magnitude 
of the Fixed Stars from the quantity of Light which 
they afford us, and the particular circumstances of 
their situation." Phil. Trans, vol. 57 (l 767), p. 234. 
Herschel's reference to this paper has been referred 
to ante, p. 95. Later references will be found in 
Todhunter's History of the Mathematical Theory of 
Probability (1865), where it is stated that the paper 
had "attracted considerable attention." MichelFs 
method of enquiry is there quoted and his results are 
given (pp. 332, 393, 491). 

8 See R. Grant, History of Physical Astronomy, 

PP- 543, 558, 559- 

3 Grant, op. cit. p. 547. 

9 8 



most fundamental fact of stellar cosmo- 
gony, the existence of physically-con- 
nected stellar groups. In the case of the 
conspicuous pairs of adjacent stairs (the 
so-called double stars) he anticipated that 
orbital revolution round each other, 
owing to their mutual gravitation, would 
in time be detected, a prediction after- 
wards brilliantly realised on a grand scale 
by Sir William Herschel. He even 
pointed out that knowledge of the period 
of their orbital revolution, combined 
with their distance from the solar sys- 
tem, would provide means of determining 
the mass of such a stellar pair in com- 
parison with the mass of the Sun 1 , a 
problem which is being worked out 
into exact knowledge by aid of refined 
determinations of parallax in our own 
time. 

" These considerations occur in the 
course of discussion of a plan for esti- 
mating the distances of the stars by com- 

1 Phil. Tram. 1784, p. 36, et $eq. 

99 



paring their brightness with that of the 
Sun, on the assumption that they give 
out an amount of light not greatly differ- 
ent from his. This method had, it seems 1 , 
been first suggested by James Gregory ; 
it was applied roughly by Huygens to 
Sirius ; and it attracted the attention of 
Lambert and later of Olbers, as well as 
that of Michell. In MichelFs argument 
the planet Saturn, whose size and distance 
are known from the Newtonian theory, 
and whose brightness relative to the Sun 
could thus be estimated, was used as an 
intermediary ; for it would be impossible 
to compare directly the dazzling bright- 
ness of the Sun with the amount of light 
received from a star. These astronomers 
all agree in assigning a parallax less than 
half a second of arc to the brightest stars; 
and this is in fact near the values that are 
now known for the very few nearest stars, 
which are thus at a distance from our 
system of about a million times that of 

1 Grant, op. clt. p. 547. 
IOO 



the Earth from the Sun, while most stars 
are very many times more remote. 

" Michell was the first 1 to propound,, 
in the same Memoir, just views as to the 
simple proportionality between the faint- 
ness of the stars just visible in a telescope 
and the area of its aperture, no other 
circumstance being essentially concerned. 
He initiated the application of this prin- 
ciple to the estimation of the distribution 
of the stars at different distances in the 
depths of space, a task afterwards carried 
out so tenaciously and brilliantly in the 
'star-gauging' of Sir William Herschel. 
He concluded from a discussion of proba- 
bilities that the bright stars were more 
numerous around our system than a uni- 
form distribution in the celestial spaces 
would permit ; and he inferred that most 
of the bright stars that did not obviously 
belong to star-groups were our nearer 
neighbours, and constituted a stellar 
system of which our own solar system is 

1 Grant, *p. at. p. 543. 

IOI 



a part ; while the fainter stars in the 
depths of space may be grouped in other 
stellar systems. Thus he thought the 
nebulae were separated universes of stars, 
so far away as to defy resolution into 
their components. Modern astronomical 
theories are now moving, of course far 
more definitely, along similar lines, forti- 
fied by the immense masses of facts 
relating to distances, motions and con- 
stitutions of the stars and nebulae, which 
are provided by the photographic plate 
and the spectroscope in conjunction with 
large telescopes. 

" In Michell's day the available data 
were utterly inadequate to guide to safe 
statistical conclusions on matters of such 
delicate inference. But the mathematical 
modes of reasoning in his Memoir of 1767 
are still of much interest in the light of 
modern knowledge, especially as they are 
illustrated by a discussion of the group of 
the Pleiades, as it is presented to the naked 
eye and also in telescopes of various aper- 
102 



tures. It may be claimed that these modes 
of reasoning give Michell a place as the 
early pioneer in the great modern problem 
of the configuration and structure of the 
universe, which first rose to prominence 
twenty years afterwards, by the labours 
of Sir William Herschel, founded on 
similar views. 

"In regard, to optics, Michell was a 
thoroughgoing Newtonian, as was natural 
in his time. Light for him consisted of 
corpuscles projected from the luminous 
body, rather than waves propagated 
through an aether. He even thought 
that, like everything material, they must 
be subject to gravitation ; and he de- 
veloped a speculation that the velocities 
of the corpuscles shot out from one of the 
larger stars must be sensibly diminished 
by the backward pull of its attraction, 
and thus be more deviated by a glass prism, 
a supposition which he proposed to test. 
At the end of his Memoir of 1767 (p. 261) 
he even suggests that the c twinkling of 

103 



the fixed stars' is due to the small number 
of luminous corpuscles received by the 
eye which might be only a few per second. 
These corpuscular optical speculations 
now carry special interest as a curiously 
definite foreshadowing of the work on 
electric radio-activity, in which Thomson , 
Rutherford and others have actually con- 
trolled the velocities of the electric cor- 
puscles by the agency of field of force, and 
have directly counted the numbers of 

r 

them that are shot out from active matter. 
" In his wide outlook over the field of 
nature, in the extent of knowledge that 
was linked together in his active interests, 
Michell was a true disciple of the British 
school of physical science, the con- 
temporary members of which were largely 
his personal friends. They were falling 
behind in mathematical analysis, owing 
to too conservative partiality for the 
geometrical methods of their master 
Newton. While the great analysts of the 
continent were closely engaged in the 
104 



expansion of the infinitesimal calculus and 
its improvement by application to the 
verification and prediction of the motions 
of the solar system, the mathematicians 
of Britain had time for wider, though less 
intricate contemplation of the correlations 
of natural phenomena, not seldom leading 
into general views which subsequent times 
were to develop with fuller knowledge." 



105 



INDEX 



Astronomy, MichelFs contributions to, 91105 

Balderton, 67 

Baxter, on the immateriality of the Soul, 81 

Birch, Dr T., 1 1 

Blagden, Sir Charles, 46, 49, 55, 60, 63 

Boscovich, R. G., 80, 83 

Boys, C. V., 90 

Bridport, 60 

Brotherton, 66 

Castle Howard, 63 

Cavendish, Hon. Henry, 3, 12, 20, 45, 47, 59, 

84-90 

Chalk, 60, 63, 64, 66 
Coulomb, C. A. de, 87, 97 
Dorchester, 60 
Dunstable, 63 

Earth, determination of mean density of, 84 
Earthquakes, Michell on, 25-39 
Exeter, 62 
Faraday, M., 83 
Farey, John, 65, 66 
Fitton, Dr, 70 
Fitzpatrick, Rev. T. C., 4 
Forbes, James David, 89 
Foston, 55, 56 
Gault, 66 

Geology, Michell's contributions to, 24-58 
Grantham, 54, 67 
Greetham Common, 50 

1 06 



Gunnerby Hill, 55, 56, 63 

Hadley, Prof. J., 1 1 

Haldon Hill, 62 

Herschel, Sir William, 14, 19, 91-96, 101, 103 

Homberg, M., 79 

Humber, 63 

Knight, Dr Gowin, 1 1, 74 

Larmor, Sir Joseph, 96 

Leeds, 76 

Lias, 53, 61, 62, 66, 67 

Light, Michell's conception of, 79, 103 

Lyell, Sir Charles, 69 

Lyme, 61 

Magnetism, Michell on, 73 

Mairan, M., 79 

Maty, Dr i\l., 1 1 

Michell, John, earliest account of, 3 ; at Queens' 
College, Cambridge, 4-6 ; Woodwardian Pro- 
fessor of Geology, 6 ; his personal appearance, 7 ; 
Fellow of Queens', ** ; his treatise on Magnets, 
8, 73; his Essay on Earthquakes, 9, 25; elected 
into the Royal Society, 1 1, 73 ; Rector ot Comp- 
ton, 12; his Marriage, 12 ; Rector of Havant, 13; 
his daughter, 13, 14; family traditions, 13; Rec- 
tor of Thornhill, 13; his connection with London, 
2O ; his early interest in geology, 21; his death 
and epitaph at Thornhill, 23 

His contributions to Geology, 24-58 ; on the 
causes and phenomena of Earthquakes, 25 ; on 
the structure of the stratified part of the Earth's 
crust, 39; his contributions to Physics, 72-90; 
on Magnetism, 73 ; on V ision, Light, etc., 76 ; 
on the immateriality of Matter, 81 ; his Torsion- 
balance for determining the mean density of the 
Earth, 84; his contributions to Astronomy, 91- 
105 

107 



Minehead, 62 

Physics, Michell's contributions to, 72-90 

Priestley, Joseph, 3, 76, 77, 78-83 

Queens' College, Cambridge, 3, 14 

Roch Abbey, 66 

Royal Society, 2, 7, 9, 10, 20, 25, 73, 76, 94 

Royal Society Club, 2, 2O, 58, 94 

Scarborough, 68 

Selenite, 53 

Sherewood Forest, 66 

Sid mouth, 6 1 

Sills or Intrusive Sheets, 37 

Smeaton, John, 65 

Smith, William, 68 

Stars, twinkling of, 103 

Strachey, John, 39 

Thornhill Rectory, 13, 22, 23, 58, 76, 95 

Thorpe, Sir T. Edward, 46 

Torsion-balance of Michell, 84, 89, 96 

Tuxford, 66 

Vapour, subterranean, 29, 36 

Vision, Light, etc., Michell on, 76-83 

Watchett, 62 

Wernerian geognosy, 27 

Whin Sill of North England, 38 

Whittakcr, Prof. E. T., 72, 83 

Wilson, George, biographer of Cavendish, 3, 47 

Wollaston, F. J. Hyde, 85 

Woodward, John, 6, 40 

Wray, Dr D., 1 1 

" Yellow Limestone/' (Jurassic) 48, 60, (Permian) 

56, 63, 64 
Zittel, K. A. von, 70 



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